The present invention relates to an anti-skid control system for use in an automotive vehicle, and in particular to an anti-skid control system for controlling braking force applied to road-wheels in braking operation to prevent the road-wheels from being locked.
In general, in an anti-skid control system, braking force is set to be adjusted for setting an adequate slip rate on the basis of a speed of each road-wheel, an acceleration, and an estimated speed of a vehicle body. One example of such anti-skid control system is disclosed in Japanese Patent Laid-open Print No. Sho 56-53945 published in 1981. In this anti-skid control system, in order to establish a slip rate of about 15%, the braking pressure is controlled for the adjustment of each road-wheel.
Normally, a deceleration of the road-wheel is increased as the slip rate becomes higher, and is tuned to be decreased after passing its maximum value, as indicated by a graph "A" in FIG. 10. However, if the road is a snow-covered one or a gravel covered one which establishes a shorter braking distance in spite of a slip rate, the slip rate is subject to increase to 100% as shown in a graph "B" in FIG. 10. Thus, when the slip rate is set to be about 15%, sometimes the braking distance may become longer than that when the road-wheel is in the locked condition.